Error when trying to modify the response of a method assigned to a public static final config variable about byte-buddy

[raphw]

What's your interceptor class, including annotations and imports?

[jwalor]

Hi , thanks for replying,
Is it technically possible to modify this method?

--> Code:
`import io.confluent.kafka.schemaregistry.rest.SchemaRegistryConfig;
import io.confluent.rest.RestConfigException;
import javassist.NotFoundException;
import net.bytebuddy.agent.ByteBuddyAgent;
import net.bytebuddy.agent.builder.AgentBuilder;
import net.bytebuddy.asm.MemberSubstitution;
import net.bytebuddy.description.type.TypeDescription;
import net.bytebuddy.dynamic.DynamicType;
import net.bytebuddy.matcher.ElementMatchers;
import net.bytebuddy.utility.JavaModule;
import org.apache.kafka.common.config.ConfigDef;

import java.lang.instrument.Instrumentation;
import java.security.ProtectionDomain;
import java.util.Properties;
import static net.bytebuddy.matcher.ElementMatchers.*;

public class MainX2 {

public static void main(String[] args) throws RestConfigException, NotFoundException {
    SchemaRegistryConfig test = new SchemaRegistryConfig(new Properties());
    Instrumentation instrumentation = ByteBuddyAgent.install();
    new AgentBuilder.Default()
            .with(AgentBuilder.RedefinitionStrategy.RETRANSFORMATION)
            .with(AgentBuilder.RedefinitionStrategy.REDEFINITION)
            .with(AgentBuilder.RedefinitionStrategy.Listener.StreamWriting.toSystemError())
            .with(AgentBuilder.Listener.StreamWriting.toSystemError().withTransformationsOnly())
            .with(AgentBuilder.InstallationListener.StreamWriting.toSystemError())
            .type(ElementMatchers.named("io.confluent.kafka.schemaregistry.rest.SchemaRegistryConfig"))
            .transform(new AgentBuilder.Transformer() {
                @Override
                public DynamicType.Builder<?> transform(DynamicType.Builder<?> builder, TypeDescription typeDescription,
                                                        ClassLoader classLoader, JavaModule module, ProtectionDomain protectionDomain) {
                    try {
                        return builder
                                .visit(MemberSubstitution.strict()
                                        .method(named("baseSchemaRegistryConfigDef"))
                                        .replaceWith(MainX2.class.getMethod("baseSchemaRegistryConfigDef"))
                                        .on(any()));
                    } catch (NoSuchMethodException e) {
                        throw new RuntimeException(e);
                    }
                  
                }
            }).installOn(instrumentation);

    SchemaRegistryConfig teSchemaRegistryConfig = new SchemaRegistryConfig(new Properties());

    System.out.println(teSchemaRegistryConfig.baseSchemaRegistryConfigDef().configKeys().size());

}

public static ConfigDef baseSchemaRegistryConfigDef() {
    return new ConfigDef();
}

`
I would like to know if it is possible to replace the body of that method with a modified one. I have tried some examples but no success.

[raphw]

It is, but the static initializer will not be rerun on a retransformation. In this case, you would need to hook before the class is loaded for the first time.

[jwalor]

I agree Rafael, with AgentBuilder could I achieve it?
If you have any reference it would help me a lot for what I am looking for

[raphw]

You mean rerun the static initializer? That is not possible, unfortunately, the JVM does not support it.

[jwalor]

If I understood what you indicated... ("you would need to hook before the class is loaded for the first time.")
could you give me some reference on how I could resolve this case? thank you so much :)

[jwalor]

@raphw
Could you just tell me which api to use?

[raphw]

You are doing it right, but there's nothing that can fix your problem if the initializer already ran.

[jwalor]

Thank you very much for the support! , I found everything about bytebuddy interesting.